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Evil twins and the multiverse: distinguishing the world of difference between epistemic and physical possibility


Physicists Brian Greene and Max Tegmark both make variants of the claim that if the universe is infinite and matter is roughly uniformly distributed that there are infinitely many “people with the same appearance, name and memories as you, who play out every possible permutation of your life choices.” In this paper I argue that, while our current best theories in astrophysics may allow one to conclude that we have infinitely many duplicates whose lives are identical to our own from start to finish, without either further advances in physics or advances in fields like biology, psychology, neuroscience, and philosophy, Greene’s and Tegmark’s claims about the ways in which our duplicates lives will differ from our own are not a consequence of our best current scientific theories. Rather, I argue that Greene and Tegmark’s conclusions rely on philosophically imprecise usages of the language of “possibility.”

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  1. Greene (2011), p. 10.

  2. Tegmark (2003), p. 41.

  3. Tegmark (2003), p. 41.

  4. Greene (2011), pp. 10–36.

  5. For a philosophical criticism of Tegmark’s version of DP, see Porpora (2013), and for a philosophical defense see Curtis (2015).

  6. Tegmark (2003), p. 41.

  7. Greene (2011), pp. 34–35.

  8. An alternative way to understand the scenarios that follow in a friendlier manner to a physical reductionist would be to claim that the observations that follow about what seem to be macro-level limiting factors at least indicate that there are additional laws of physics we’ve yet to discover that provide for additional physical limitations on what matter arrangements are physically possible. I will suppress this alternative way of framing the observations for the time being but will return to it later.

  9. Green (2011), p. 33.

  10. For a taste of the debate surrounding the causal closure of physics and whether the special sciences can ultimately be reduced to physics or not, see Papineau (2009) in favor of reduction and Fodor (1997) against. I currently favor the anti-reductionist view, which perhaps explains why I have been drawn to organizing my argument the way that I have. But one who embraces the causal closure of physics and a physical reductionist view can just as easily raise qualms with Tegmark and Greene’s arguments for ETP by showing how they’ve helped themselves to saying all sort of states of affairs are possible without providing physical explanations for how these states of affairs could arise.

  11. Thanks to Christina Conroy, Ioan Muntean, and especially Chapman Waters for useful conversations on matters related to this paper. And thanks to the two anonymous reviewers from this journal for their extremely helpful and insightful comments.


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Correspondence to Mark Satta.

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Satta, M. Evil twins and the multiverse: distinguishing the world of difference between epistemic and physical possibility. Synthese 198, 1153–1160 (2021).

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